Failed to use X as non-privileged user on AS 3.0
 

I recently installed Redhat AS 3.0 and have no problem log in as root user. However, whenever I tried to log in as non-privileged user, the Gnome desktop started with blue background, menubar, but nothing else. I have no popup menu from right-clicking the mouse. If I tried to start any application from the pull-down menu, a window appears on the screen saying:

Can't launch entry
Details: Failed to fork (Resource temporarily unavailable)

If I checked the /var/log/messages file, I saw the following messages:

modprobe: modprobe: Can't locate module char-major-10-134
kernel: hde: dma_intr: status=0x51 { DriveReady SeekComplete Error }
kernel: hde: dma_intr: error=0x84 { DriveStatusError BadCRC }

If I used "ulimit -a", everything seems normal. So what might go wrong here? Thanks in advance.